XeLaTeX and graphicx don't seem to work well

Question

I am having trouble getting the graphicx package to work well when running XeLaTeX on my MAC. I am including .jpg files; some of them scale very nicely, but others don't.

Here is the MWE

\documentclass[11pt]{book}
\usepackage{graphicx}
\begin{document}
\includegraphics[width=1in]{behistun_photo.jpg}
\includegraphics[width=2in]{behistun_photo.jpg} 
\includegraphics[width=1in]{graphics/Ishango_IRSNB.jpg} 
\includegraphics[width=2in]{graphics/Ishango_IRSNB.jpg} 
\end{document}

When I compile using PDFLaTeX, it works just fine. The images are scaled properly. When I compile using XeLaTeX, the first jpg file scales properly, but not the second. In addition, the image in the second one over-writes the lines above. It seems that it is setting the correct space for the scaled picture, but then inserting a much larger one.